Method of effacing zipper image

ABSTRACT

A method of effacing zipper image, applicable to scan a document by a scanner with a stagger charge-coupled device. The nth (n is a positive integer) pixel obtained by scan on a scan line at which the zipper image is produced is subtracted by the (n+1)th pixel obtained by scan on the scan line. The absolute value of the result is then compared to a critical value. If the result is smaller than the critical value, the nth pixel is the nth pixel modified as the nth pixel after process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a method of effacing zipper image,and more particularly, to a method of effacing zipper image byapproximating the gray scales of two neighboring pixels.

2. Description of the Related Art

FIG. 1 shows a block diagram of a scanner having a staggercharge-coupled device. In FIG. 1, the scanner 100 is coupled to acomputer 150. The scanner comprises a stagger charge-coupled device 110with a primary line and a secondary line, an application specificintegrated circuit (ASIC) 120, an image compensation buffer 130 and anI/O interface 140.

When the scanner having the stagger charge-coupled device is scanning adocument, the pitch between the primary line and the secondary line issmall. The primary line is thus affected by the light reflected from thesecondary line. Similarly, the secondary line is also affected by thelight reflected from the primary line. A zipper image (as shown in FIG.3) in addition to a real image (as shown in FIG. 2) is thus produced byusing the scanner with the stagger charge-coupled device to scan thedocument. When a document has a black-and-white boundary, the zipperimage is more obvious, causing error in the actual image. Currently, amethod to compensate the zipper image has not been found in the priorart.

SUMMARY OF THE INVENTION

The invention provides a method of effacing a zipper image byapproximating the gray scales of two neighboring pixels.

The method of effacing the zipper image provided by the invention isapplicable to scan a document using a scanner with a staggercharge-coupled device. The nth pixel obtained by scan on a scan line atwhich the zipper image is produced is subtracted by the (n+1)th pixelobtained by scan on the scan line. The absolute value of the subtractionresult is compared to a critical value. When the result is smaller thanthe critical value, the nth pixel is modified as the nth pixel afterprocess. If the result is larger than the critical value, no process isperformed.

The processed nth pixel is one half of the sum of the nth pixel obtainedby scan and the (n+1)th pixel obtained by scan.

In one embodiment of the present invention, the nth pixel after beingprocessed is the sum of one half of the nth pixel obtained by scan andone half of the (n+1)th pixel obtained by scan.

In one embodiment of the present invention, the critical value is apredetermined value or produced by a logic circuit. The critical valuecan be adjusted according to the modulation transfer function of thescanner with the stagger charge-coupled device.

Both the foregoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a scanner with a stagger charge-coupleddevice;

FIG. 2 shows a real image of a document;

FIG. 3 shows a zipper image produced by scanning the document using ascanner with a stagger charge-coupled device; and

FIG. 4 shows a flow chart for a method of effacing a zipper image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a compensation operation is performed on a documentbefore the document is scanned by a scanner 100 with a staggercharge-coupled device 110. Thereby, an image compensation parameter isobtained and stored in a computer 150. When the stagger charge-coupleddevice 110 performs the scan on any part of the document, an imagecompensation parameter corresponding to the scanned part is retrievedfrom the computer 150 and transmitted to the image compensation buffer130 via the I/O interface 140. The staggered scanned image obtained fromthe stagger scan by the stagger charge-coupled device 110 is thencorrected by the ASIC 120 according to the image compensation parametertransmitted from the image compensation buffer 130. The corrected imageis then transmitted to the computer 150 via the I/O interface 140 forstorage.

However, as the distance between the primary line and the secondary lineis very short, the primary line is affected by the light reflected fromthe secondary line. Similarly, the secondary line is also affected bythe light reflected from the primary line. A zipper image is thusproduced to cause an error between the scanned image and the real image.

FIG. 4 shows a flow chart of effacing a zipper image according to theinvention. In the following embodiment, a critical value used in theeffacing process of the zipper image can be a predetermined value or avalue generated by a logic circuit. In FIG. 4, assume that the nth (n isa positive integer) pixel obtained by scan on the scan line at which thezipper is produced is P_(n), and the (n+1)th pixel obtained by scan onthe scanning line is P_(n+1). The nth pixel being processed is referredas P_(n)′, and the critical value is denoted as T. In this embodiment,whether P_(n) subtracted by P_(n+1) is smaller than T is determined instep s400. When the absolute value of |P_(n)−P_(n+1)| is smaller than T,P_(n) is modified as P_(n)′. The value of P_(n) ^(′) can be expressed as(P_(n)+P_(n+1))/2 or (½)P_(n)+(½)P_(n+1), as shown in step s410. The nthpixel after being processed as P_(n)′ approximates the gray values ofthe nth and (n+1)th pixel P_(n) and P_(n+1) obtained by scan, so thatthe zipper image can be effaced. When |P_(n)−P_(n+1)| is larger than T,the effacing process is not performed.

The above embodiment compares two neighboring pixels at a scan line atwhich the zipper image is produced with a critical value as a referencefor effacing process. If the effacing process is required, the grayvalues of these two neighboring pixels are approximated to each other toreduce the zipper image. However, the modulation transfer function ofthe scanner with the stagger charge-coupled device is slightly reduced.

According to the above, the invention has the following advantages:

1. Only a critical value is required to determine whether an effacingprocess is performed, thereby, two gray scales of two neighboring pixelsare approximated to each other, and the zipper image is effaced.

2. The fabrication cost is not increased.

Other embodiments of the invention will appear to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples to be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

1. A method to effacing a zipper image, applicable to scan a documentusing a scanner with a stagger charge-coupled device, the methodcomprising: determining whether the absolute value of a result ofsubtracting a nth pixel obtained by scan on a scan line on which thezipper image is produced by a (n+1)th pixel obtained by scan on the scanline is smaller than a critical value; and modifying the nth pixelobtained by scan as a nth pixel after being processed if the result issmaller than the critical value.
 2. The method according to claim 1,wherein the nth pixel after being processed equals to one half of a sumof the nth pixel and the (n+1)th pixel obtained by scan.
 3. The methodaccording to claim 1, wherein the nth pixel after being processed equalsto one half of the nth pixel obtained by scan plus one half of the(n+1)th pixel obtained by scan.
 4. The method according to claim 1,wherein the nth pixel obtained by scan is not processed if the result islarger than the critical value.
 5. The method according to claim 1,wherein the critical value is a predetermined value.
 6. The methodaccording to claim 1, wherein the critical value can be adjustedaccording to the modulation transfer function of the scanner with thestagger charge-coupled device.